The invention is directed to a process and an apparatus for measuring the quenching intensity of liquid quenching baths, especially salt baths by introducing into the bath a test body which has been heated to a temperature higher than the bath temperature.
The quenching after austenitization in the heat treatment of steels represents an important step in the termination of the process. The liquid baths such as oil or water baths used for this purpose thereby can have various quenching rates, effectiveness, or intensities depending on their temperature, composition, movement of the bath, and possible sludge. Above all, this is true for the so-called heating bath, a salt melt made of alkali nitrates and nitrites.
Besides the motion of the bath and the sludge content, a decisive condition is played by the water content of the salt melt. A water content of 1% can increase the quenching intensity, e.g. to double the amount.
Therefore the testing of the quenching intensity of these baths is indispensable in order to produce the necessary hardness results in the heat treatment of steels. Previously the methods of testing depended essentially on copying the quenching process. A test body was heated to hardening temperature and then cooled in the quenching bath, in which case the cooling time was measured for a fixed temperature interval. the test bodies can be constructed either with very poor heat capacity and very good heat conductivity as silver balls or can be present as massive steel bodies which react very slowly to the quenching. This test method is very cumbersome and practically unusable for continuous supervision of the quenching intensity of the baths if it is a question of obtaining an immediate test result for a controller which should influence the quenching intensity, e.g. by addition of water.
Therefore it is the object of the present invention to provide a process and apparatus for measuring the quenching intensity of liquid quenching baths, especially salt baths by inserting into the bath a test body heated to a temperature above the bath temperature whereby the measurement device reacts quickly, is suited to a continuous supervision, and should yield a controlled signal representing the measured value.